An antenna is probably the most important part of making a wireless connection. The three main types you'll be seeing: omnidirectional antennas, they typically look like just a stick just one long element and omnidirectional they're emitting into all directions around them equally that's if i'm looking onto the horizontal plane that would just be an even distribution to all sides seen from the side not so much seen from the side there will be a distinct direction we'll see one in a moment patch panel and sector antennas are somewhat directional think piece of cake something like 45 60 degrees maybe 90 degrees opening looking like a piece of cake or a white beam or something like that and then lastly highly directional antennas are grits parables dishes they make really sharp beams ultimately not just the line they still have a certain opening beam width but they're quite directed it's almost it's like a torch that you direct in in one particular direction then there's antennas that are so small that we can barely see them they're built into stuff their print antennas on the left here you see this typical meandering like winding river print that's a wi-fi print antenna on a very small iot device here same in mobile phones there isn't a lot of space and you have to fit in a lot of antennas wi-fi cellular antennas bluetooth so they're printed antennas very small we typically don't see them here's another popular simple antenna it's a monopole antenna it's just a quarter wavelength piece of wire with four counterparts and the ground plane described many many years ago 125 years ago and it gives us a gain of 5 dbi theoretically when we build it properly the monopole antenna and this is an omnidirectional antenna seen from the top it would be a circle seen from the side and here in this 3d view um we often say it's a donut if a donut is something you're eating well you'll recognize the donut structure here seen from the side there is distinct directions in which it sends its power seen from the top it's a circle note that it sometimes tilts a little bit this preferred direction to the side doesn't always have to be straight horizontal it can go up or down that's what we call tilt in antennas the parabol antenna based on a really really really old idea mathematically if you find a surface for which each incoming beam is reflected to the same point imagine you're putting like a dish into the sun like a mirror dish into the sun and then that it would concentrate all the sunbeams into one point that's actually something we're using in solar cookers solar ovens then that surface that's described as a parable the mathematical the finding of this is centuries old 200 bc i found as the date for that as a radio reflector also more than 100 years old that is basically what a dish a parable antenna is doing and you find them in closed types like those dishes you sometimes you also use for tv and radio signals you find them in grid forms benefit here is not so much wind resistance when the wind blows dishes need to be really really strong to stand that power of the wind grids are better here and they do the same for the electrical the electromagnetic signal so that's a grid antenna here's another small one that you often find built into mobile phones or iot devices and stuff it's a two-dimensional antenna it's it's got a plane but also like an f-shape on top of it often found like i said in embedded boards and such it's small you can make it a lot smaller than say a quarter wavelength so you can fit it into these small devices here's a picture of how these different antennas go into a mobile phone a co-linear antenna is a combination of several pieces of dipole pieces combined together in interchanging polarities so the effects actually add up that's why we call them co linear many linear elements in one and that gives us an omni directional antenna this is by far the most common type we see for omnidirectional users and from the outside they just look like a stick basically this is the radiation pattern for the omni antenna we've seen it before roughly like a doughnut circle from above and a squeezed something seen from the side directing into two distinct favorite directions horizontal or if it's off the horizontal we speak of a tilt this is what commercial sector antennas look like they're a combination of several patches inside so they're actually like a long square and the resulting pattern is a wide beam into one distinct direction wide beam can mean anything from 30 degrees 44 45 60 degrees something like that this would be the radiation pattern for a uh such a sector antenna wide seen from the in the horizontal plane here and looking at the elevation and for the two polarities you see a relatively sharp relatively thin beam width here's another pattern for many of you might have seen the sort of patch on the wall type of antenna often with the access point integrated into it this would be the radiation patterns for such a type antenna note that it's actually not strongest towards the center but the directions of strongest signals are kind of off center around it so don't direct it directly at where you want to go it it spreads out the signal it's meant to ideally sit on the ceiling perhaps on a wall but its main usage would be overhead on ceiling a little comment on choice of antennas don't always go for the strongest um here's an example of we've chosen a very very strong directional antenna but if we want to hit all of this building here we actually don't want such a strong directional antenna we want a spread we want a wider beam width probably looking at this picture we want 60 to 90 degrees not a thin line we want to have a relatively weak directional behavior in order to hit all the flaws of this building here's one more little um look at how we're choosing antennas let's say we have this case we have a person behind the house this is who we want to reach we have an omni antenna behind that building obviously that's not a very good solution our first reaction is well bring it up bring it onto a tower that's somewhat better however now we have the problem that we're missing the receiving side we're missing the user our next reaction to that is we'll use an omnidirectional with a tilt down that's better however most of our power is still going into directions where we don't need it at all so our next improvement would be to use a sector antenna instead of the tilted omni make such drawings when you're planning antennas they're very very useful just pen and paper try to you need to know where your users are where you are the receiving end of your signal you need to know where you want to put your antenna what places are available accessible to you and then you just make drawings and until you find the good idea for what type of antenna would be best to choose here's a sector antenna again and one more reminder very often these days you actually see antenna and access point integrated into one or it's kind of like the other way around the antenna has been hidden inside the access point it's integrated somewhere and the whole thing comes in one enclosure and these commercial sector antennas they can have more or less complicated patterns look at them when you deploy a specific type check whether the drawing you just made kind of fits together with the device that you are deploying so look at those patterns and also reminder a good wireless device antenna or integrated access point antenna comes with this information cheap home user stuff often doesn't if at all possible try to use equipment that gives you this information.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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